Friction welding is commonly or widely used as a joining method. in a manufacture of gas turbines. Friction welding is a method within the group of so-called pressure welding methods. Friction welding permits joining or interconnecting structural components by friction. In connection with linear friction welding, one of the structural components is moved back and forth in a translatory direction whereas the other structural component is stationary and pressed with a certain force against the moving structural component. During the friction welding, the joining surfaces of the structural components to be joined or interconnected adapt to each other by heat forging. The linear friction welding is considered to be part of the so-called oscillating friction welding methods. Further friction welding methods include the so-called rotation friction welding and the so-called turning or stirring friction welding.
In connection with a conventional procedure for joining or interconnecting structural components by oscillating friction welding, namely a linear friction welding, the two components to be joined to each other are rubbed against one another whereby one structural component is moved back and forth in a translatory direction while preferably a defined upsetting pressure is applied to the joining surface through the other structural component of the two components. Reference can be made in this regard for example to U.S. Pat. No. 6,219,916 and U.S. Pat. No. 6,095,402. During applying the friction motion to the structural components to be joined, the two joining surfaces do not always coincide. Rather, free surface areas where there is no overlap occur temporarily in a marginal zone of the surfaces to be joined. These temporarily free surface areas are exposed to a possible contamination, for example, if the linear friction welding is performed under the normal atmosphere, the free non-overlapping surface areas are exposed to contamination by oxygen whereby brittle phases can occur in the joining zone between the two structural components to be joined. Such brittle phases impair the material strength of the junction or joint.
In order to avoid such contaminations by oxygen, it is known to perform the linear friction welding in a protective gas atmosphere, for example in an argon atmosphere. However, it has been found that even when the linear friction welding is performed in an argon atmosphere, contaminations or faults can occur in the junction or joining zone. Such faults involve the formation of hose-shaped or tubular pores filled with argon gas. These argon filled hose pores remain while applying the upsetting pressure. Such hose pores may have a negative effect on the so-called vibration or oscillation strength of the junction or joining zone produced by linear friction welding.